SEMINAR REPORT ON

ARCHITECTURAL AND STRUCTURAL DESIGNBLAST RESISTANT BUILDINGS

A seminar report submitted in partial fulfillment of the requirementsfor the award of the degree of

Bachelor of Technologyin

Civil Engineering

Submitted ByPAUL JOMY (SYAKECE033)

Under The Guidence OfMr. ARUN.K.A M.Tech (Geotechnical)

Eighth Semester 2010 Admission

Sreepathy Institute of Management & TechnologyVavanoor, Palakkad-679533

Affiliated toUniversity Of Calicut

Department of Civil EngineeringSreepathy Institute of Management & Technology

Vavanoor, Palakkad-679533

BONAFIDE CERTIFICATE

This is to certify that the seminar entitled ”ARCHITECTURAL AND STRUCTURALDESIGN BLAST RESISTANT BUILDINGS” is a bonafide record of the seminarpresented by PAUL JOMY (Reg No. SYAKECE033) under our supervision andguidance. The seminar report has been submitted to the Department of Civil Engi-neering of SIMAT Vavanoor, Palakkad-679533 in partial fulfillment of the award ofthe Degree of Bachelor of Technology in Civil Engineering, during the year 2013-2014.

Mr. ARUN.K.AGuideAsst. ProfessorCivil EnggSIMAT, Vavanoor

Internal ExaminerDate :

Mr. SUDHEER.K.VHead of the DeptCivil EnggSIMAT, VavanoorPalakkad

External ExaminerDate :

ABSTRACT

The increase in the number of terrorist attacks especially in the last few years hasshown that the effect of blast loads on buildings is a serious matter that should be takeninto consideration in the design process. Although these kinds of attacks are excep-tional cases, man-made disasters; blast loads are in fact dynamic loads that need to becarefully calculated just like earthquake and wind loads.

The objective of this study is to shed light on blast resistant building design the-ories, the enhancement of building security against the effects of explosives in botharchitectural and structural design process and the design techniques that should becarried out. Firstly, explosives and explosion types have been explained briefly. Inaddition, the general aspects of explosion process have been presented to clarify theeffects of explosives on buildings. To have a better understanding of explosives andcharacteristics of explosions will enable us to make blast resistant building designmuch more efficiently. Essential techniques for increasing the capacity of a building toprovide protection against explosive effects is discussed both with an architectural andstructural approach.

ACKNOWLEDGEMENT

I am extremely thankful to our Principal Dr.S.P. SUBRAMANIAN for giving his con-sent for this seminar. And also i’m thankful to Mr. SUDHEER.K.V, Head of theDepartment of Civil engineering, for his valuable suggestions and support. The valu-able help and encouragement rended in this endeavour by my guide Mr. ARUN.K.A,Asst.Professors, Dept.of Civil Engineering for his constant help and support through-out the presentation of the seminar by providing timely advices and guidance. I thankGod almighty for all the blessing received during this endeavor. Last, but not least Ithank all my friends for the support and encouragement they have given me during thecourse of my work.

Contents

List of Figures iii

1 Introduction 11.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.2 Objective Of The Blast Design . . . . . . . . . . . . . . . . . . . . . 1

2 Literature survey 32.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32.2 Explosion - Major of All Terrorist Activities . . . . . . . . . . . . . . 3

2.2.1 Expected Terrorist Blast On Structures . . . . . . . . . . . . . 32.2.2 Major Cause of Life Loss After The Blast . . . . . . . . . . . 3

2.3 Goals of Blast Resistant Design . . . . . . . . . . . . . . . . . . . . 42.4 Basic Requirements To Resist Blast Loads . . . . . . . . . . . . . . . 4

2.4.1 Mechanics of a Conventional Explosion . . . . . . . . . . . . 42.5 Types of Explosions . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

2.5.1 Unconfined Explosion . . . . . . . . . . . . . . . . . . . . . 52.5.2 Confined Explosions . . . . . . . . . . . . . . . . . . . . . . 6

2.6 Explosion Process For High Explosive . . . . . . . . . . . . . . . . . 6

3 Architectural Aspect of Blast Resistant Building Design 93.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93.2 Planning And Layout . . . . . . . . . . . . . . . . . . . . . . . . . . 93.3 Structural Form and Internal Layout . . . . . . . . . . . . . . . . . . 93.4 Bomb Shelter Areas . . . . . . . . . . . . . . . . . . . . . . . . . . . 113.5 Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113.6 Glazing And Cladding . . . . . . . . . . . . . . . . . . . . . . . . . 123.7 Floor Slabs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123.8 Columns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133.9 Transfer Girders . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133.10 External Treatments . . . . . . . . . . . . . . . . . . . . . . . . . . . 143.11 Facade And Atrium . . . . . . . . . . . . . . . . . . . . . . . . . . . 143.12 Overall Lateral Building Resistance, Shear Walls . . . . . . . . . . . 143.13 Lower Floor Exterior . . . . . . . . . . . . . . . . . . . . . . . . . . 143.14 Stand Off Distance . . . . . . . . . . . . . . . . . . . . . . . . . . . 153.15 Internal Explosion Threat . . . . . . . . . . . . . . . . . . . . . . . . 15

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4 Structural Aspect of Blast Resistant Building 174.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174.2 Structural Failure . . . . . . . . . . . . . . . . . . . . . . . . . . . . 194.3 Comparison of Blast And Seismic Loading . . . . . . . . . . . . . . 204.4 Damage Evaluation Procedure For Building Subjected To Blast Impact 21

5 Case Study 235.1 World Trade Center Collapse . . . . . . . . . . . . . . . . . . . . . . 23

5.1.1 The Design . . . . . . . . . . . . . . . . . . . . . . . . . . . 235.1.2 The Details of The Impact . . . . . . . . . . . . . . . . . . . 24

5.1.2.1 The Airplane Impact . . . . . . . . . . . . . . . . . 245.1.2.2 The Collapse . . . . . . . . . . . . . . . . . . . . . 27

5.1.3 Can Building Resist Direct Airplane Hits . . . . . . . . . . . 285.1.4 How Can We Minimize The Chance of Progressive Collapse . 29

5.2 Israel as a Case Study And Paradigm . . . . . . . . . . . . . . . . . . 29

6 Conclusion 34

References 36

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List of Figures

2.1 Air burst with ground reflections . . . . . . . . . . . . . . . . . . . . 52.2 Surface burst . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62.3 Fully vented, partially vented and fully confined explosions . . . . . . 62.4 Blast wave pressures plotted against time . . . . . . . . . . . . . . . 7

3.1 Schematic layout of site for protection against bombs . . . . . . . . . 103.2 Internal planning of a building . . . . . . . . . . . . . . . . . . . . . 11

4.1 Sequence of air-blast effects . . . . . . . . . . . . . . . . . . . . . . 174.2 Enhanced beam-to-column connection details for steelwork and rein-

forced concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 184.3 Shock Front from Air Burst . . . . . . . . . . . . . . . . . . . . . . . 204.4 Shock Front from Surface Burst . . . . . . . . . . . . . . . . . . . . 20

5.1 A cutaway view of WTC structure . . . . . . . . . . . . . . . . . . . 245.2 A graphic illustration of WTC . . . . . . . . . . . . . . . . . . . . . 255.3 Airplane’s impact on WTC . . . . . . . . . . . . . . . . . . . . . . . 265.4 Collapse of WTC . . . . . . . . . . . . . . . . . . . . . . . . . . . . 275.5 Entrance to an underground shelter in Israel . . . . . . . . . . . . . . 305.6 Shelter used as a playroom . . . . . . . . . . . . . . . . . . . . . . . 315.7 Shelter used as a playroom . . . . . . . . . . . . . . . . . . . . . . . 315.8 The change from underground shelters to protected spaces . . . . . . 325.9 Example of Israeli structural blast design . . . . . . . . . . . . . . . . 325.10 Example of Israeli structural blast design . . . . . . . . . . . . . . . . 335.11 Example of traditional American structual blast design . . . . . . . . 33

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Chapter 1

Introduction

1.1 General

The increase in the number of terrorist attacks especially in the last few years hasshown that the effect of blast loads on buildings is a serious matter that should be takeninto consideration in the design process. Although these kinds of attacks are excep-tional cases, man-made disasters; blast loads are in fact dynamic loads that need to becarefully calculated just like earthquake and wind loads.

The objective of this study is to shed light on blast resistant building design the-ories, the enhancement of building security against the effects of explosives in botharchitectural and structural design process and the design techniques that should becarried out. Firstly, explosives and explosion types have been explained briefly. Inaddition, the general aspects of explosion process have been presented to clarify theeffects of explosives on buildings. To have a better understanding of explosives andcharacteristics of explosions will enable us to make blast resistant building designmuch more efficiently. Essential techniques for increasing the capacity of a building toprovide protection against explosive effects is discussed both with an architectural andstructural approach.

Damage to the assets, loss of life and social panic are factors that have to be min-imized if the threat of terrorist action cannot be stopped. Designing the structures tobe fully blast resistant is not an realistic and economical option, however current en-gineering and architectural knowledge can enhance the new and existing buildings tomitigate the effects of an explosion.

1.2 Objective Of The Blast Design

The primary objectives for providing blast resistant design for buildings are:

-Personnel safety-Controlled shutdown

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-Financial consideration

Blast resistant design should provide a level of safety for persons in the buildingthat is no less than that for persons outside the buildings in the event of an explosion.Evidence from past incidents has shown that many of the fatalities and serious injurieswere due to collapse of buildings onto the persons inside the building. This objectiveis to reduce the probability that the building itself becomes a hazard in an explosion.

Preventing cascading events due to loss of control of process units not involved inthe event is another objective of blast resistant design. An incident in one unit shouldnot affect the continued safe operation or orderly shutdown of other units.

Preventing or minimizing financial losses is another objective of blast resistantdesign. Buildings containing business information, critical or essential equipment,expensive and long lead time equipment, or equipment which if destroyed, would con-stitute significant interruption or financial loss to the owner should be protected.

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Chapter 2

Literature survey

2.1 General

The need and requirements for blast resistance in buildings have evolved over recentyears. Buildings have become more complex and have increased in size thus increas-ing the risk of accidental explosions. Such explosions have demolished the buildings,in some cases resulting in substantial personnel causalities and business losses. Suchevents have heightened the concerns of the industry, plant management, and regula-tory agencies about the issues of blast protection in buildings have the potential forexplosions. Generally, these issues relate to plant building safety and risk manage-ment to prevent or minimize the occurrence of such incidents and to siting, design, andoperations.

2.2 Explosion - Major of All Terrorist Activities

The probability that any single building will sustain damage from accidental or delib-erate explosion is very low, but thecost for those who are unprepared is very high.

2.2.1 Expected Terrorist Blast On Structures

-External car bomb-Internal car bomb-Internal package-Suicidal car bombs

2.2.2 Major Cause of Life Loss After The Blast

-Flying debris-Broken glass-Smoke and fire-Blocked glass-Power loss-Communications breakdown-Progressive collapse of structure

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2.3 Goals of Blast Resistant Design

The goals of blast-resistant design are to :

-Reduce the severity of injury-Facilitate rescue-Expedite repair-Accelerate the speed of return to full operation.

2.4 Basic Requirements To Resist Blast Loads

To resist blast loads,

- The first requirement is to determine the threat. The major threat is caused byterrorist bombings. The threat for a conventional bomb is defined by two equallyimportant elements, the bomb size, or charge weight, and the standoff distance - theminimum guaranteed distance between the blast source and the target.

- Another requirement is to keep the bomb as far away as possible, by maximizingthe keepout distance. No matter what size the bomb, the damage will be less severethe further the target is from the source.

- Structural hardening should actually be the last resort in protecting a structure;detection and prevention must remain the first line of defense . As terrorist attacksrange from the small letter bomb to the gigantic truck bomb as experienced in Okla-homa City, the mechanics of a conventional explosion and their effects on a target mustbe addressed.

2.4.1 Mechanics of a Conventional Explosion

With the detonation of a mass of TNT at or near the ground surface, the peak blast pres-sures resulting from this hemispherical explosion decay as a function of the distancefrom the source as the ever-expanding shock front dissipates with range. The incidentpeak pressures are amplified by a reflection factor as the shock wave encounters an ob-ject or structure in its path. Except for specific focusing of high intensity shock wavesat near 45 incidence, these reflection factors are typically greatest for normal incidence(a surface adjacent and perpendicular to the source) and diminish with the angle ofobliquity or angular position relative to the source. Reflection factors depend on theintensity of the shock wave, and for large explosives at normal incidence these reflec-tion factors may enhance the incident pressures by as much as an order of magnitude.

Charges situated extremely close to a target structure impose a highly impulsive,high intensity pressure load over a localized region of the structure; charges situatedfurther away produce a lower-intensity, longer-duration uniform pressure distribution

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over the entire structure. In short by purely geometrical relations, the larger the stand-off, the more uniform the pressure distribution over the target. Eventually, the entirestructure is engulfed in the shock wave, with reflection and diffraction effects creatingfocusing and shadow zones in a complex pattern around the structure. Following theinitial blast wave, the structure is subjected to a negative pressure, suction phase andeventually to the quasi-static blast wind. During this phase, the weakened structuremay be subjected to impact by debris that may cause additional damage

2.5 Types of Explosions

Mainly there are two types of explosions

2.5.1 Unconfined Explosion

Unconfined explosions can occur as an air-burst or a surface burst. In an air burst

Figure 2.1: Air burst with ground reflections

explosion, the detonation of the high explosive occurs above the ground level andintermediate amplification of the wave caused by ground reflections occurs prior to thearrival of the initial blast wave at a building Figure 2.1.

As the shock wave continues to propagate outwards along the ground surface, afront commonly called a Mach stem is formed by the interaction of the initial waveand the reflected wave.

However a surface burst explosion occurs when the detonation occurs close to oron the ground surface. The initial shock wave is reflected and amplified by the groundsurface to produce a reflected wave. Figure 2.2. Unlike the air burst, the reflected wavemerges with the incident wave at the point of detonation and forms a single wave. Inthe majority of cases, terrorist activity occurres in built-up areas of cities, where de-

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vices are placed on or very near the ground surface.

Figure 2.2: Surface burst

2.5.2 Confined Explosions

When an explosion occurs within a building, the pressures associated with the initialshock front will be high and therefore will be amplified by their reflections within thebuilding.

Figure 2.3: Fully vented, partially vented and fully confined explosions

This type of explosion is called a confined explosion. In addition and dependingon the degree of confinement, the effects of the high temperatures and accumulationof gaseous products produced by the chemical reaction involved in the explosion willcause additional pressures and increase the load duration within the structure.

Depending on the extent of venting, various types of confined explosions are pos-sible. Figure2.3

2.6 Explosion Process For High Explosive

An explosion occurs when a gas, liquid or solid material goes through a rapid chemi-cal reaction. When the explosion occurs, gas products of the reaction are formed at a

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very high temperature and pressure at the source. These high pressure gasses expandrapidly into the surrounding area and a blast wave is formed. Because the gases aremoving, they cause the surrounding air move as well. The damage caused by explo-sions is produced by the passage of compressed air in the blast wave. Blast wavespropagate at supersonic speeds and reflected as they meet objects. As the blast wavecontinues to expand away from the source of the explosion its intensity diminishes andits effect on the objects is also reduced. However, within tunnels or enclosed passages,the blast wave will travel with very little diminution.

Close to the source of explosion the blast wave is formed and violently hot andexpanding gases will exert intense loads which are difficult to quantify precisely. Oncethe blast wave has formed and propagating away from the source, it is convenientto separate out the different types of loading experienced by the surrounding objects.Three effects have been identified in three categories. The effect rapidly compressingthe surrounding air is called air shock wave. The air pressure and air movement effectdue to the accumulation of gases from the explosion chemical reactions is called dy-namic pressure and the effect rapidly compressing the ground is called ground shockwave.

Figure 2.4: Blast wave pressures plotted against time

The air shock wave produces an instantaneous increase in pressure above the ambi-ent atmospheric pressure at a point some distance from the source. This is commonlyreferred to as overpressure. As a consequence, a pressure differential is generated be-tween the combustion gases and the atmosphere, causing a reversal in the direction offlow, back towards the center of the explosion, known as a negative pressure phase.This is a negative pressure relative to atmospheric , rather than absolute negative pres-sure Figure 2.4. Equilibrium is reached when the air is returned to its original state.

As a rough approximation, 1kg of explosive produces about 1m3 of gas. As thisgas expands, its act on the air surrounding the source of the explosion causes it to move

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and increase in pressure. The movement of the displaced air may affect nearby objectsand cause damage. Except for a confinement case, the effects of the dynamic pressurediminish rapidly with distance from source.

The ground shock leaving the site of an explosion consists of three principal com-ponents . A compression wave which travels radially from the source; a shear wavewhich travels radially and comprises particle movements in a plane normal to the ra-dial direction where the ground shock wave intersects with the surface and a surface orRaleigh wave. These waves propagate at different velocities and alternate at differentfrequencies.

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Chapter 3

Architectural Aspect of Blast Resistant Building Design

3.1 General

The target of blast resistant building design philosophy is minimizing the consequencesto the structure and its inhabitants in the event of an explosion. A primary requirementis the prevention of catastrophic failure of the entire structure or large portions of it.It is also necessary to minimize the effects of blast waves transmitted into the build-ing through openings and to minimize the effects of projectiles on the inhabitants ofa building. However, in some cases blast resistant building design methods, conflictswith aesthetical concerns, accessibility variations, fire fighting regulations and the con-struction budget restrictions.

3.2 Planning And Layout

Much can be done at the planning stage of a new building to reduce potential threatsand the associated risks of injury and damage. The risk of a terrorist attack, necessity ofblast protection for structural and non-structural members, adequate placing of shelterareas within a building should be considered for instance. In relation to an externalthreat, the priority should be to create as much stand-off distance between an externalbomb and the building as possible. On congested city centers there may be little orno scope for repositioning the building, but what small stand-off there is should besecured where possible. This can be achieved by strategic location of obstructionssuch as bollards, trees and street furniture. Figure 4.1 shows a possible external layoutfor blast safe planning.

3.3 Structural Form and Internal Layout

Structural form is a parameter that greatly affects the blast loads on the building.Arches and domes are the types of structural forms that reduce the blast effects onthe building compared with a cubicle form. The plan-shape of a building also has asignificant influence on the magnitude of the blast load it is likely to experience. Com-plex shapes that cause multiple reflections of the blast wave should be discouraged.Projecting roofs or floors, and buildings that are U-shaped on plan are undesirable for

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Figure 3.1: Schematic layout of site for protection against bombs

this reason. It should be noted that single story buildings are more blast resistant com-pared with multi-story buildings if applicable.

Partially or fully embed buildings are quite blast resistant. These kinds of struc-tures take the advantage of the shock absorbing property of the soil covered by. Thesoil provides protection in case of a nuclear explosion as well.

The internal layout of the building is another parameter that should be undertakenwith the aim of isolating the value from the threat and should be arranged so that thehighest exterior threat is separated by the greatest distance from the highest value asset.Foyer areas should be protected with reinforced concrete walls; double-dooring shouldbe used and the doors should be arranged eccentrically within a corridor to prevent theblast pressure entering the internals of the building. Entrance to the building should becontrolled and be separated from other parts of the building by robust construction forgreater physical protection. An underpass beneath or car parking below or within thebuilding should be avoided unless access to it can be effectively controlled.

A possible fire that occurs within a structure after an explosion may increase thedamage catastrophically. Therefore the internal members of the building should bedesigned to resist the fire.

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Figure 3.2: Internal planning of a building

3.4 Bomb Shelter Areas

The bomb shelter areas are specially designated within the building where vulnerabil-ity from the effects of the explosion is at a minimum and where personnel can retirein the event of a bomb threat warning. These areas must afford reasonable protectionagainst explosions; ideally be large enough to accommodate the personnel involvedand be located so as to facilitate continual access. For modern-framed buildings, shel-ter areas should be located away from windows, external doors, external walls and thetop floors if the roof is weak. Areas surrounded by full-height concrete walls shouldbe selected and underground car parks, gas storage tanks, areas light weight partitionwalls, e.g. internal corridors, toilet areas, or conference should be avoided while lo-cating the shelter areas. Basements can sometimes be useful shelter areas, but it isimportant to ensure that the building does not collapse on top of them. The functionalaspects of a bomb shelter area should accommodate all the occupants of the building;provide adequate communication with outside; provide sufficient ventilation and san-itation; limit the blast pressure to less than the ear drum rupture pressure and providealternative means of escape.

3.5 Installation

Gas, water, steam installations, electrical connections, elevators and water storage sys-tems should be planned to resist any explosion affects. Installation connections arecritical points to be considered and should be avoided to use in high-risk deformationareas. Areas with high damage receiving potential e.g. external walls, ceilings, roofslabs, car parking spaces and lobbies also should be avoided to locate the electricaland other installations. The main control units and installation feeding points shouldbe protected from direct attacks. A reserve installation system should be provided fora potential explosion and should be located remote from the main installation system.

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3.6 Glazing And Cladding

Glass from broken and shattered windows could be responsible for a large number ofinjuries caused by an explosion in a city centre. The choice of a safer glazing materialis critical and it has been found out that laminated glass is the most effective in thiscontext. On the other hand, applying transparent polyester anti-shatter film to the innersurface of the glazing is as well an effective method.

For the cladding, several aspects of design should be considered to minimize thevulnerability of people within the building and damage to the building itself. Theamount of glazing in the facade should be minimized. This will limit the amount ofinternal damage from the glazing and the amount of blast that can enter. It shouldalso be ensured that the cladding is fixed to the structure securely with easily accessi-ble fixings. This will allow rapid inspection after an explosion so that any failure ormovement can be detected.

3.7 Floor Slabs

Treatments for conventional flat slab design are as follows:

1. More attention must be paid to the design and detailing of exterior bays and lowerfloors, which are the most susceptible to blast loads.

2. In exterior bays/lower floors, drop panels and column capitols are required to shortenthe effective slab length and improve the punching shear resistance.

3. If vertical clearance is a problem, shear heads embedded in the slab will improve theshear resistance and improve the ability of the slab to transfer moments to the columns.

4. The slab-column interface should contain closed-hoop stirrup reinforcement prop-erly anchored around flexural bars within a prescribed distance from the column face.

5. Bottom reinforcement must be provided continuous through the column. This rein-forcement serves to prevent brittle failure at the connection and provides an alternatemechanism for developing shear transfer once the concrete has punched through.

6. The development of membrane action in the slab, once the concrete has failed at thecolumn interface, provides a safety net for the postdamaged structure. Continuouslytied reinforcement, spanning both directions, must be detailed properly to ensure thatthe tensile forces can be developed at the lapped splices. Anchorage of the reinforce-ment at the edge of the slab is required to guarantee the development of the tensileforces.

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3.8 Columns

Treatment for conventionally designed columns to improve blast resisting mechanism:

1. The potential for direct lateral loading on the face of the columns, resulting from theblast pressure and impact of explosive debris, requires that the lower-floor columns bedesigned with adequate ductility and strength.

2. The perimeter columns supporting the lower floors must also be designed to re-sist this extreme blast effect.

3. Encasing these lower-floor columns in a steel jacket will provide confinement, in-crease shear capacity, and improve the columns’ ductility and strength. An alternative,which provides similar benefits, is to embed a steel column within the perimeter con-crete columns or wall section.

4. The possibility of uplift must be considered, and, if deemed likely, the columnsmust be reinforced to withstand a transient tensile force.

5. For smaller charge weights, spiral reinforcement provides a measure of core con-finement that greatly improves the capacity and the behavior of the reinforced concretecolumns under extreme load.

3.9 Transfer Girders

The building relies on transfer girders at the top of the atrium to distribute the loads ofthe columns above the atrium to the adjacent columns outside the atrium. The transfergirder spans the width of the atrium, which insures a column-free architectural spacefor the entrance to the building.

Transfer girders typically concentrate the load-bearing system into a smaller num-ber of structural elements. This loadtransfer system runs contrary to the concept ofredundancy desired in a blast environment. The column connections, which supportthe transfer girders, are to provide sustained strength despite inelastic deformations.The following recommendations must be met for transfer girders:

1. The transfer girder and the column connections must be properly designed anddetailed, using an adequate blast loading description.

2. A progressive-collapse analysis must be performed, particularly if the blast load-ing exceeds the capacity of the girder.

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3.10 External Treatments

The two parameters that most directly influence the blast environment that the structurewill be subjected to are the bomb’s charge weight and the standoff distance. Of thesetwo, the only parameter that anyone has any control over is the standoff distance.

3.11 Facade And Atrium

The facade is comprised of the glazing and the exterior wall. Better glazing has alreadybeen discussed above and wall obviously should be hardened to resist the loading.Presence of an atrium along the face of the structure will require two protective mea-sures. On the outside of the structure, the glass and glass framing must be strengthenedto withstand the loads. On the inside, the balcony parapets, spandrel beams, and ex-posed slabs must be strengthened to withstand the loads that enter through the shatteredglass.

3.12 Overall Lateral Building Resistance, Shear Walls

The ability of structures to resist a highly impulsive blast loading depends on the ductil-ity of the load-resisting system.This means that the structure has to be able to deform inelastically under extreme overload, thereby dissipating large amounts of energy, priorto failure.. In addition to providing ductile behavior for the structure, the followingprovisions would improve the blast protection capability of the building:

1. Use a well-distributed lateral-load resisting mechanism in the horizontal floor plan.This can be accomplished by using several shear walls around the plan of the buildingthis will improve the overall seismic as well as the blast behavior of the building.

2. If adding more shear walls is not architecturally feasible, a combined lateral-loadresisting mechanism can also be used. A central shear wall and a perimeter moment-resisting frame will provide for a balanced solution. The perimeter momentresistingframe will require strengthening the spandrel beams and the connections to the outsidecolumns. This will also result in better protection of the outside columns.

Several recommendations were presented for each of the identified features. Theimplementation of these recommendations will greatly improve the blast-resisting ca-pability of the building under consideration.

3.13 Lower Floor Exterior

The architectural design of the building of interest currently calls for window glassaround the first floor. Unless this area is constructed in reinforced concrete, the dam-age to the lower floor structural elements and their connections will be quite severe.

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Consequently, the injury to the lower floor inhabitants will be equally severe. In gen-eral, two sizes of charges can be discussed

1. To protect against a small charge weight, a nominal 300 mm (12 in.) thick wallwith 0.3 percent steel doubly reinforced in both directions might be required.

2. For intermediate charge weight protection, a 460 mm (18 in.) thick wall with 0.5percent steel might be needed.

3.14 Stand Off Distance

The keep out distance, within which explosives-laden vehicles may not penetrate, mustbe maximized and guaranteed. As we all know, the greater the standoff distance, themore the blast forces will dissipate resulting in reduced pressures on the building. Sev-eral recommendations can be made to maintain and improve the standoff distance forthe building under consideration:

1. Use anti-ram bollards or large planters, placed around the entire perimeter. Thesebarriers must be designed to resist the maximum vehicular impact load that could beimposed. For maximum effectiveness, the barriers-bollards or planters-must be placedat the curb.

2. The public parking lot at the corner of the building must be secured to guarantee theprescribed keepout distance from the face of the structure. Preferably, the parking lotshould be eliminated.

3. Street parking should not be permitted on the near side of the street, adjacent tothe building.

4. An additional measure to reduce the chances of an attack would be to preventparking on the opposite side of the street. While this does not improve the keep outdistance, it could eliminate the ”parked” bomb, thereby limiting bombings to Park andrun.

3.15 Internal Explosion Threat

The blast environment could be introduced into the interior of the structure in four vul-nerable locations:

The entrance lobby, the basement mechanical rooms, the loading dock, and theprimary mail rooms. Specific modifications to the features of these vulnerable spacescan prevent an internal explosion from causing extensive damage and injury inside thebuilding.

1. Walls and slabs adjacent to the lobby, loading dock, and mail rooms must be

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hardened to protect against the hand delivered package bomb, nominally a 10-20 kgexplosive. This hardening can be achieved by redesigning the slabs and erecting cast-in-place reinforced-concrete walls, with the thickness and reinforcement determinedrelative to the appropriate threat.

2. The basement must be similarly isolated from all adjacent occupied office space,including the floor above, from the threat of a small package bomb.

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Chapter 4

Structural Aspect of Blast Resistant Building

4.1 General

The front face of a building experiences peak overpressures due to reflection of an ex-ternal blast wave. Once the initial blast wave has passed the reflected surface of thebuilding, the peak overpressure decays to zero. As the sides and the top faces of thebuilding are exposed to overpressures (which has no reflections and are lower than thereflected overpressures on the front face), a relieving effect of blast overpressure isexperienced on the front face. The rear of the structure experiences no pressure untilthe blast wave has traveled the length of the structure and a compression wave hasbegun to move towards the centre of the rear face. Therefore the pressure built up isnot instantaneous. On the other hand, there will be a time lag in the development ofpressures and loads on the front and back faces.

This time lag causes translational forces to act on the building in the direction ofthe blast wave.

Figure 4.1: Sequence of air-blast effects

Blast loadings are extra ordinary load cases however, during structural design, thiseffect should be taken into account with other loads by an adequate ratio. Similar tothe static loaded case design, blast resistant dynamic design also uses the limit state

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design techniques which are collapse limit design and functionality limit design. Incollapse limit design the target is to provide enough ductility to the building so that theexplosion energy is distributed to the structure without overall collapse. For collapselimit design the behavior of structural member connections is crucial. In the case ofan explosion, significant translational movement and moment occur and the loads in-volved should be transferred from the beams to columns. The structure doesnt collapseafter the explosion however it cannot function anymore.

Functionality limit design however, requires the building to continue functional-ity after a possible explosion occurred. Only non-structural members like windowsor cladding may need maintenance after an explosion so that they should be designedductile enough.

When the positive phase of the shock wave is shorter than the natural vibrationperiod of the structure, the explosion effect vanishes before the structure responds.This kind of blast loading is defined as impulsive loading. If the positive phase islonger than the natural vibration period of the structure, the load can be assumed con-stant when the structure has maximum deformation. This maximum deformation is afunction of the blast loading and the structural rigidity. This kind of blast loading isdefined as quasi-static loading. Finally, if the positive phase duration is similar to thenatural vibration period of the structure, the behavior of the structure becomes quitecomplicated. This case can be defined as dynamic loading. Frame buildings designed

Figure 4.2: Enhanced beam-to-column connection details for steelwork and reinforcedconcrete

to resist gravity, wind loads and earthquake loads in the normal way have frequently

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been found to be deficient in two respects. When subjected to blast loading; the fail-ure of beam-to-column connections and the inability of the structure to tolerate loadreversal.Beam-to-column connections can be subjected to very high forces as the resultof an explosion. These forces will have a horizontal component arising from the wallsof the building and a vertical component from the differential loading on the upper andlower surfaces of floors. Providing additional robustness to these connections can be asignificant enhancement.

In the connections, normal details for static loading have been found to be inade-quate for blast loading. Especially for the steelwork beam-to-column connections, it isessential for the connection to bear inelastic deformations so that the moment framescould still operate after an instantaneous explosion. Figure 2.8 shows the side-plateconnection detail in question . The main features to note in the reinforced concreteconnection are the use of extra links and the location of the starter bars in the connec-tion Figure 2.8. These enhancements are intended to reduce the risk of collapse or theconnection be damaged, possibly as a result of a load reversal on the beam.

It is vital that in critical areas, full moment-resisting connections are made in orderto ensure the load carrying capacity of structural members after an explosion. Beamsacting primarily in bending may also carry significant axial load caused by the blastloading.

On the contrary, columns are predominantly loaded with axial forces under normalloading conditions, however under blast loading they may be subjected to bending.Such forces can lead to loss of load-carrying capacity of a section. In the case of anexplosion, columns of a reinforced concrete structure are the most important membersthat should be protected. Two types of wrapping can be applied to provide this. Wrap-ping with steel belts or wrapping with carbon fiberreinforced polymers (CFRP).

Cast-insitu reinforced concrete floor slabs are the preferred option for blast resis-tant buildings, but it may be necessary to consider the use of precast floors in somecircumstances. Precast floor units are not recommended for use at first floor where therisk from an internal explosion is greatest. Lightweight roofs and more particularly,glass roofs should be avoided and a reinforced concrete or precast concrete slab is tobe preferred.

4.2 Structural Failure

An explosion will create blast wave. The air-blast shock wave is the primary dam-age mechanism in an explosion. The pressures it exerts on building surfaces may beseveral orders of magnitude greater than the loads for which the building is designed.The shock wave will penetrate and surround a structure and acts in directions that thebuilding may not have been designed for, such as upward force on the floor system.In terms of sequence of response, the air-blast first impinges on the weakest point inthe vicinity of the device closest to the explosion, typically the exterior envelope of

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the building. The explosion pushes on the exterior walls at the lower stories and maycause wall failure and window breakage. As the shock wave continues to expand, itenters the structure, pushing both upward and downward on the floor slabs

Figure 4.3: Shock Front from Air Burst

Figure 4.4: Shock Front from Surface Burst

4.3 Comparison of Blast And Seismic Loading

Blast wave and seismic loading are two different type of extreme force that may causestructural failure. However, they share some common similarities. Similarities be-tween seismic and blast loading includes the following:

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1. Dynamic loads and dynamic structural response.

2. Involve inelastic structural response.

3. Design considerations will focus on life safety as opposed to preventing structuraldamage.

4. Other considerations: Nonstructural damage and hazards.

5. Performance based design: life safety issues and progressive collapse.

6. Structural integrity: includes ductility, continuity, and redundancy; balanced design.

The differences between these two types of loading include:

1. Blast loading is due to a propagating pressure wave as opposed to ground shak-ing.

2. Blast results in direct pressure loading to structure; pressure is in all directions,whereas a Seismic event is dominated by lateral load effects.

3. Blast loading is of higher amplitude and very short duration compared with a seis-mic event.

4. Magnitude of blast loading is difficult to predict and not based on geographicallocation.

5. Blast effects are confined to structures in the immediate vicinity of event becausepressure decays rapidly with distance; local versus regional even.

6. Progressive collapse is the most serious consequence of blast loading.

4.4 Damage Evaluation Procedure For Building Subjected To Blast Impact

1.Slab failure is typical in blasts due to large surface area subjected to upward pressurenot considered in gravity design.

2. Small database on blast effects on structures.

3.Seismic-resistant design is mature compared with blast-resistant design.

In summary, while the effect of blast loading is localized compared with an earth-quake, the ability to sustain local damage without total collapse (structural integrity) isa key similarity between seismic-resistant and blast-resistant design. In this study, the

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evaluation data that had been listed in inspection form is adapted and modified frominspection form for building after an earthquake. Even though, seismic loading willcause global response to building compared to blast loading which will cause local-ized response, but similar damage assessment procedure could be used.

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Chapter 5

Case Study

5.1 World Trade Center Collapse

The collapse of the World Trade Center (WTC) towers on September 11, 2001, was assudden as it was dramatic; the complete destruction of such massive buildings shockednearly everyone. Immediately afterward and even today, there is widespread specula-tion that the buildings were structurally deficient, that the steel columns melted, or thatthe fire suppression equipment failed to operate. In order to separate the fact from thefiction, I have attempted to quantify various details of the collapse.

The major events include the following:

The airplane impact with damage to the columns. The ensuing fire with loss of steelstrength and distortion (figure 5.3)The collapse, which generally occurred inward without significant tipping.(figure 5.4)Before going to the details it is useful to review the overall design of the towers

5.1.1 The Design

The towers were designed and built in the mid-1960s through the early 1970s eachtower was 64 m square, standing 411 m above street level and 21 m below grade. Thisproduces a height-to-width ratio of 6.8. The total weight of the structure was roughly500,000 t. The building is a huge sail that must resist a 225 km/h hurricane. It wasdesigned to resist a wind load of 2 kPaa total of lateral load of 5,000 t.

In order to make each tower capable of withstanding this wind load, the architectsselected a lightweight perimeter tube design consisting of 244 exterior columns of 36cm square steel box section on 100 cm centers(figure 3). This permitted windows morethan one-half meter wide. Inside this outer tube there was a 27 m 40 m core, which wasdesigned to support the weight of the tower. It also housed the elevators, the stairwells,and the mechanical risers and utilities. Web joists 80 cm tall connected the core to theperimeter at each story. Concrete slabs were poured over these joists to form the floors.In essence, the building is an egg-crate construction, i.e. 95 percent air. The egg-crateconstruction made a redundant structure (i.e., if one or two columns were lost, the

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Figure 5.1: A cutaway view of WTC structure

loads would shift into adjacent columns and the building would remain standing). TheWTC was primarily a lightweight steel structure; however, its 244 perimeter columnsmade it one of the most redundant and one of the most resilient skyscrapers.

5.1.2 The Details of The Impact

5.1.2.1 The Airplane Impact

The early news reports noted how well the towers withstood the initial impact of theaircraft; however, when one recognizes that the buildings had more than 1,000 timesthe mass of the aircraft and had been designed to resist steady wind loads of 30 timesthe weight of the aircraft, this ability to withstand the initial impact is hardly surprising.Furthermore, since there was no significant wind on September 11, the outer perimetercolumns were only stressed before the impact to around 1/3 of their 200 MPa designallowable.

The only individual metal component of the aircraft that is comparable in strengthto the box perimeter columns of the WTC is the keel beam at the bottom of the aircraftfuselage. While the aircraft impact undoubtedly destroyed several columns in the WTCperimeter wall, the number of columns lost on the initial impact was not large and theloads were shifted to remaining columns in this highly redundant structure. Of equalor even greater significance during this initial impact was the explosion when 90,000Lgallons of jet fuel, comprising nearly 1/3 of the aircrafts weight, ignited. The ensuingfire was clearly the principal cause of the collapse (see figure 5.2)

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Figure 5.2: A graphic illustration, from the USA Today newspaper web site, of theWorld Trade Center points of impact.

The fire is the most misunderstood part of the WTC collapse.Even today, the me-dia report (and many scientists believe) that the steel melted. It is argued that the jetfuel burns very hot, especially with so much fuel present. This is not true. Part ofthe problem is that people often confuse temperature and heat. While they are related,they are not the same. Thermodynamically, the heat contained in a material is relatedto the temperature through the heat capacity and the mass. Temperature is defined asan intensive property, meaning that it does not vary with the quantity of material, whilethe heat is an extensive property, which does vary with the amount of material. Oneway to distinguish the two is to note that if a second log is added to the fireplace, thetemperature does not double; it stays roughly the same, but the length of time the fireburns, doubles and the heat so produced is doubled. Thus, the fact that there were90,000 L of jet fuel on a few floors of the WTC does not mean that this was an unusu-ally hot fire. The temperature of the fire at the WTC was not unusual, and it was mostdefinitely not capable of melting steel.

In combustion science, there are three basic types of flames, namely, a jet burner,a pre-mixed flame, and a diffuse flame. A jet burner generally involves mixing thefuel and the oxidant in nearly stoichiometric proportions and igniting the mixturein a constant-volume chamber. Since the combustion products cannot expand in theconstant-volume chamber, they exit the chamber as a very high velocity, fully com-

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Figure 5.3: Flames and debris exploded from the World Trade Center south towerimmediately after the airplanes impact. The black smoke indicates a fuel-rich fire

busted, jet. This is what occurs in a jet engine, and this is the flame type that generatesthe most intense heat.

In a pre-mixed flame, the same nearly stoichiometric mixture is ignited as it exits anozzle, under constant pressure conditions. It does not attain the flame velocities of ajet burner. An oxyacetylene torch or a Bunsen burner is a premixed flame.

In a diffuse flame, the fuel and the oxidant are not mixed before ignition, but flowtogether in an uncontrolled manner and combust when the fuel/oxidant ratios reachvalues within the flammable range. A fireplace flame is a diffuse flame burning in air,as was the WTC fire. Diffuse flames generate the lowest heat intensities of the threeflame types.

If the fuel and the oxidant start at ambient temperature, a maximum flame temper-ature can be defined. For carbon burning in pure oxygen, the maximum is 3,200C;for hydrogen it is 2,750C. Thus, for virtually any hydrocarbons, the maximum flametemperature, starting at ambient temperature and using pure oxygen, is approximately3,000C. This maximum flame temperature is reduced by two-thirds if air is used ratherthan pure oxygen. The reason is that every molecule of oxygen releases the heat of

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formation of a molecule of carbon monoxide and a molecule of water. If pure oxy-gen is used, this heat only needs to heat two molecules (carbon monoxide and water),while with air, these two molecules must be heated plus four molecules of nitrogen.Thus, burning hydrocarbons in air produces only one-third the temperature increase asburning in pure oxygen because three times as many molecules must be heated whenair is used. The maximum flame temperature increase for burning hydrocarbons (jetfuel) in air is, thus, about 1,000Chardly sufficient to melt steel at 1,500C.

5.1.2.2 The Collapse

Figure 5.4: Collapse of WTC

Nearly every large building has a redundant design that allows for loss of one pri-mary structural member, such as a column. However, when multiple members fail, theshifting loads eventually overstress the adjacent members and the collapse occurs likea row of dominoes falling down.

The perimeter tube design of the WTC was highly redundant. It survived the lossof several exterior columns due to aircraft impact, but the ensuing fire led to othersteel failures. Many structural engineers believe that the weak pointswere the angleclips that held the floor joists between the columns on the perimeter wall and the corestructure .With a 700 Pa floor design allowable, each floor should have been able tosupport approximately 1,300 t beyond its own weight. The total weight of each tower

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was about 500,000 t.

As the joists on one or two of the most heavily burned floors gave way and the outerbox columns began to bow outward, the floors above them also fell. The floor below(with its 1,300t design capacity) could not support the roughly 45,000 t of ten floors(or more) above crashing down on these angle clips. This started the domino effect thatcaused the buildings to collapse within ten seconds, hitting bottom with an estimatedspeed of 200 km per hour. If it had been free fall, with no restraint, the collapse wouldhave only taken eight seconds and would have impacted at 300 km/h.

5.1.3 Can Building Resist Direct Airplane Hits

If the design terrorist attack is similar to that of Sept. 11, can buildings be given thecapacity to meet this demand? To answer this question, it is important to understandthe physics at work when a plane in flight is stopped by a building.

If the performance objective is to resist a direct airplane hit and protect people in-side the building, the plane cannot be allowed to penetrate the exterior wall. To stop aBoeing 767 traveling in excess of 500 miles per hour in a distance of a few feet wouldtake a deceleration force in excess of 400 million pounds.

Each tower of the World Trade Center was designed for a total horizontal force(or design wind load) of about 15 million pounds. The total design wind load for amore commonly sized high-rise, say, 40 stories tall, would be about 4 million pounds.In other words, to resist the amount of force generated by a direct 767 hit, todaysbuildings would need to be 100 times stronger than dictated by code, which is bothphysically and economically impossible.

So why did the World Trade Center Towers not collapse immediately due to theimpact load on the system? The planes did not stop in a few feet, but had an effectivestopping distance of over 100 feet. This would drop the deceleration force down tosomething close to the capacity of the building. Another part of the answer to thisquestion lies in the way that the exterior of the building was structured. The exteriorcolumns were 14-inch square welded steel box columns spaced at 40 inches on center.This means that there was only 26 inches clear between each column. The columnswere integral with the steel spandrels beams and formed essentially a solid wall of steelwith perforations for windows. This wall construction was able to form a Vierendeelbridge over the hole created in one side of each of the towers.

Both of these facts that the plane was not stopped at the exterior and that thecolumns and spandrels were extremely dense were necessary to prevent the buildingfrom collapsing immediately upon impact.

Can buildings be designed for direct airplane hits? Yes and no.Yes, for small aircraft. A definite no, for large commercial aircraft.

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5.1.4 How Can We Minimize The Chance of Progressive Collapse

This is still one more question that some people are asking. Because the towers ul-timately collapsed with one floor crashing down upon the next, it has been called aprogressive collapse.

Again, it is important to think carefully about the question. Arent all collapsesprogressive? Something breaks, and then something else breaks, and so on. Normally,when the term progressive collapse is used, it specifically refers to the loss of one ortwo columns or bearing walls that cause a collapse to propagate vertically.

In the case of the World Trade Center there were about 40 columns lost on oneface of each of the towers and there was no propagation of collapse from this loss. Sodid the World Trade Center have good resistance to progressive collapse? By normaluse of the term progressive collapse it did. The collapse that did ultimately occur wasprogressive, like all collapses, but was not progressive collapse that some internationalcodes address.

The difficulty in understanding this concept is illustrated with the following story.

A New York fire chief wrote that experienced firefighters know that the buildingsthat are most susceptible to progressive collapse are buildings that are well-tied to-gether (i.e., able to transfer building loads from one element to another, such as acolumn). Yet, virtually every structural engineer will advise that one of the best waysto prevent progressive collapse is to tie the building together. How can there be thiskind of a contradiction?

The difference is that the engineer is thinking about losing a column or two and thefire chief is talking about losing a whole part of a building. As the event that initiatesthe progressive collapse becomes larger than losing a column, the risk becomes thatthe strong horizontal ties of a building will cause the collapse to propagate horizontally.

Any discussion of code provisions with respect to progressive collapse must recog-nize that both the engineer and the fire chief are right depending on the kind of hazardthat is defined.

At least six safety systems present in the World Trade Center towers were com-pletely and immediately disabled or destroyed upon impact: fireproofing, automaticsprinklers, compartmentalization and pressurization, lighting, structure and exit stairs.

5.2 Israel as a Case Study And Paradigm

Over the course of its history, Israel has adapted military blast design to blast design tobe used as a part of civilian structures. Israels methods for integrating blast protectioninto its society can be used as an example for the rest of the world as it is increasingly

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subjected to more security threats.

When the state was founded in 1948, Israel had already constructed undergroundshelters across the country (see Figure 5.5). Underground shelters were the first formsof civilian blast protection because one of the most effective methods of providingprotection for a structure is to bury it (Smith and Hetherington, 1994). Undergroundbomb shelters do have some benefits; they are generally larger than what could beprovided for inside of a building so they are more comfortable for long periods oftime. In addition , when the shelters were not in use they could be used for recreationalpurposes (Einstein, 2003 ). Many shelters were turned into libraries and meeting placesfor youth groups (see Figures 2.10 and 2.11). These underground shelters became apart of Israeli culture.

Figure 5.5: Entrance to an underground shelter in Israel

In the 1970s civilians in Israel were being threatened along its border with Lebanon.Katusha rockets were being launched over the Lebanese border into the Israeli citieson the other side, and Israel needed to provide its citizens with protection from theattacks. Throughout northern Israel rooms designed to protect a buildings inhabitantsfrom an explosion were included in most homes as well as schools and public buildings(Sandler, 2003). This was the beginning of the transition from underground shelters,separate from the buildings. To shelters integrated into daily structures.

The biggest change in Israels policy toward protecting its citizens came in 1991with the Gulf war. Saddam Hussein threatened Israel with Scud missiles and this notonly increased the treat due to explosions, but also introduced the strong possibility ofbio-chemical threats. People were now required to have protected spaces within everyhome, office, and public space. The windows had to be able to be sealed around theedges, and doors would have a wet towel placed at the bottom. The room also had to be

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Figure 5.6: Shelter used as a playroom

Figure 5.7: Shelter used as a playroom

blast proof so that in an attack craked walls and windows would not allow poisonousgas to seep in.

New building requirements to have these protected spaces in all civilian structures,and how to design these spaces were developed and known as Haga requirements (Ein-stein, 2003). These regulations were fully integrated into the Israeli building code andcontinue to be maintained in order to protect Israeli civilians.

While the regulations being put into the building code was instigated by a need toprovide protection against chemical warfare , the importance of regulating the integra-tion of protected spaces into buildings remains and extend into blast protection.

Protecting a building from explosions is now an integral part of a buildings design

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Figure 5.8: The change from underground shelters to protected spaces

Figure 5.9: Example of Israeli structural blast design

out security risks while preserving the essence of the design (Einstein, 2003). Israelisociety cannot have all of its buildings feel like concrete fortified structures even if theyrely (Figures 2.13,2.14,2.15) are examples of Israeli blast designed structures, versusthe current blast designed structures in the United States.

Since September 11, 2001 and the destruction of the World Trade Centre due toterrorism, it has become apparent that the U.S. must also change its approach to pro-tecting its citizens from explosions. Israel has successfully integrated blast protectioninto its society and buildings as a result of years of terror and threats. By makingblast protection a permanent part of the building code professionals have been forcedto come up with new ways of designing building s that protect their inhabitants butstill maintain peoples quality of life (Einstein, 2003). Because of the increased andcontinuing threat to the United States it is clear that structural engineers here too willhave to make blast design an integral part of all structures. The more this mentality is

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Figure 5.10: Example of Israeli structural blast design

Figure 5.11: Example of traditional American structual blast design

put into practice the sooner blast design will be able t coexist with current structuraldesign consideration such as architecture, sustainability, usability, and economics.

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Chapter 6

Conclusion

The aim in blast resistant building design is to prevent the overall collapse of the build-ing and fatal damages. Despite the fact that, the magnitude of the explosion and theloads caused by it cannot be anticipated perfectly, the most possible scenarios will letto find the necessary engineering and architectural solutions for it.

In the design process it is vital to determine the potential danger and the extent ofthis danger. Most importantly human safety should be provided. Moreover, to achievefunctional continuity after an explosion, architectural and structural factors should betaken into account in the design process, and an optimum building plan should be puttogether.

This study is motivated from making buildings in a blast resistant way, pioneeringto put the necessary regulations into practice for preventing human and structural lossdue to the blast and other human-sourced hazards and creating a common sense aboutthe explosions that they are possible threats in daily life. In this context, architecturaland structural design of buildings should be specially considered.

During the architectural design, the behavior under extreme compression loadingof the structural form, structural elements e.g. walls, flooring and secondary structuralelements like cladding and glazing should be considered carefully. In conventional de-sign, all structural elements are designed to resist the structural loads. But it should beremembered that, blast loads are unpredictable, instantaneous and extreme. Therefore,it is obvious that a building will receive less damage with a selected safety level anda blast resistant architectural design. On the other hand, these kinds of buildings willless attract the terrorist attacks.

Structural design after an environmental and architectural blast resistant design, aswell stands for a great importance to prevent the overall collapse of a building. Withcorrect selection of the structural system, well designed beam-column connections,structural elements designed adequately, moment frames that transfer sufficient loadand high quality material; its possible to build a blast resistant building. Every sin-gle member should be designed to bear the possible blast loading. For the existingstructures, retrofitting of the structural elements might be essential. Although these

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precautions will increase the cost of construction, to protect special buildings with ter-rorist attack risk like embassies, federal buildings or trade centers is unquestionable.

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References

[1] Koccaz Z. (2004) Blast Resistant Building Design, MSc Thesis, Istanbul Techni-cal University, Istanbul, Turkey.

[2] Smith P.D., Hetherington J.G. (1994) Blast and ballistic loading of structures.Butterworth Heinemann.

[3] Yandzio E., Gough M. (1999). Protection of Buildings Against Explosions, SCIPublication, Berkshire, U.K.

[4] Website : www.iitk.ac.in/nicee/wcee/article/14-05-01-0536.PDF

[5] Civil engineering articles at google.com

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